1. Field of the Invention
The present invention relates to a ball joint.
2. Description of the Prior Art
A link rod is shown in FIG. 4 as an example for which a conventional ball joint is used.
A link rod referred to herein has a rod portion 1 and ball joints 2 provided at both ends thereof. More precisely, the link rod includes a housing 4 made of synthetic resin, having a housing portion 3 integrally formed at each end of rod portion 1. A ball stud 5 is attached to each of housing portions 3 at the ends of housing 4.
In the same manner as in ordinary ball joints, ball joint 2 at each end of a link rod, such as the one described above, includes a ball portion 6 of ball stud 5 pressed into an inner chamber 7 of housing portion 3 where it is slidably supported. A shank portion 8, integrally formed with ball portion 6 of ball stud 5, movably protrudes from the opening of housing portion 3. Naturally, an inner diameter of an opening 9 of housing portion 3 is smaller than the outer diameter of ball portion 6 of ball stud 5 in order to resist a large load when ball portion 6 of ball stud 5 is pulled out of inner chamber 7 of housing 3. The load maximum load before ball portion 6 is withdrawn from housing portion 3 is hereinafter called the breakaway load.
Housing 4, which consists of housing portions 3 and rod portion 1, requires sufficient rigidity and strength to resist compression and/or traction in the direction parallel to rod portion 1. To attain such rigidity and strength, rod portion 1 and housing portions 3 are made sufficiently thick or include reinforcing ribs. Thick sections add weight to the part. Ribs make the part more complicated to mold.
Another way to attain rigidity and strength of housing portions 3 and rod portion 1 is to reinforce the synthetic resin used for molding these portions using reinforcing glass fiber, carbon fiber or other similar material. Such a method, however, reduces the elasticity of the synthetic resin of housing portions 3 due to the presence of the reinforcement fiber. As a result, it is difficult to separate inner chamber 7 of housing portion 3 from the mold at completion of molding. This sometimes damages or breaks housing portion 3. In addition, housing portion 3 is subject to breakage when ball portion 6 of ball stud 5 is pressed into inner chamber 7. Increasing the inner diameter of opening 9 of housing portion 3 in order to solve the above problem undesirably decreases the breakaway load of ball portion 6 of ball stud 5 from housing portion 3.
Another example of a link rod having a ball joint is shown in FIG. 5. This link rod includes a rod 11 having a ring-shaped metal holder 12 integrally formed at each end thereof. A housing 14 of ball joint 13 is supported in each metal holder 12. Housings 14 are made of synthetic resin to permit presssing of a ball portion therin. However, such configuration increases the number of parts, complicates the assembly and increases the cost.
As described above, ball joint 2 that include a housing 4 made of synthetic resin achieves its strength and rigidity at the expense of large size and heavy weight or of complicted assembly. Trying to maintain sufficient strength by reinforcing the synthetic resin with glass fiber, carbon fiber or other similar materials causes reduced breakaway load.
An object of the present invention is to provide a ball joint having a housing made of synthetic resin which consists of a housing portion and a rod portion integrally formed with the outer side of the housing portion, wherein the strength and rigidity of the housing portion and rod portion can be easily attained without reducing the breakaway load of the ball stud or increasing the size or weight.